1. Technical Field of the Invention
The invention relates to titanium dioxide- and carbonate-containing composite pigments, their manufacture and their use for improving the pigment light-scattering efficiency in coatings, plastics and laminates.
2. Description of Related Art
Inorganic pigments, and particularly titanium dioxide pigments, are often incorporated into various matrices as whiteners, tinting agents or opacifiers. Owing to its high refractive index, titanium dioxide scatters light particularly efficiently and is therefore the most important white pigment in the fields of application paint and coatings, plastics, paper and fibres. The light scattering efficiency decreases if the titanium dioxide particles dispersed in the matrix are spaced a smaller distance apart than roughly half the wavelength of the light, i.e. roughly 0.20 to 0.25 μm. The light scattering efficiency is typically measured with the help of the hiding power or the tinting strength (lightening power) of the titanium dioxide pigment in the matrix.
On the other hand, titanium dioxide is a significant cost factor, and a search has long since been in progress to find possible ways of reducing the quantity of titanium dioxide used, but without having to accept significant losses of hiding power. Savings can be achieved by combining titanium dioxide particles with suitable extenders, these extender particles being intended to act as spacers for the TiO2 particles. The known methods encompass both simple blending of the components and combination of the TiO2 particles with the extender particles by means of a precipitated binder, or in-situ precipitation of the extender on the surface of the titanium dioxide particles. Moreover, methods are known for dispersing the fine titanium dioxide particles on coarser extender particles.
Only selected documents from the available, extensive literature on the prior art are cited below.
WO 1999/035193 A1, for example, describes the manufacture of a pigment blend consisting of titanium dioxide and an inorganic extender (“spacer”), such as SiO2 or CaCO3, for use in paper production.
DE 10 057 294 C5 discloses a pigment blend consisting of titanium dioxide and talcum for use in base decorative laminating paper.
EP 0 861 299 B1 discloses a titanium dioxide pigment coated with inorganic nanoparticles, such as colloidal silica, as well as a layer of inorganic oxides, such as aluminium, silicon or zirconium oxide, where the inorganic oxide layer is either located between the titanium dioxide surface and the nanoparticles, or forms the outer coating. The inorganic nanoparticles are SiO2, Al2O3 or CaCO3.
DE 10 2006 012 564 A1 discloses titanium dioxide pigment particles with hollow microspheres and an aluminumoxide/aluminumphosphate coating on their surface.
In the method according to EP 0 956 316 B1, pigment particles and precipitated calcium carbonate (PCC) are mixed together in an aqueous phase, such that a composite pigment is obtained, in which the carbonate particles with a particle size of 30 to 100 nm are attached to the surface of the pigment particles. The composite pigment contains 30 to 90% by weight precipitated calcium carbonate.
WO 2009/109705 A1 discloses a composite pigment where the pigment particles are encased by intergrown nano particulate calcium carbonate particles.
DE 1 792 118 A1 discloses the in-situ precipitation of calcium carbonate in a titanium dioxide pigment suspension by mixing a calcium chloride and a sodium carbonate solution, where one of these solutions contains titanium dioxide pigment. This produces composite calcium carbonate/titanium dioxide particles.
WO 2000/001771 A1 discloses a composite pigment that contains inorganic particles with a particle size of roughly 1 to 10 μm, and to whose surface titanium dioxide pigment particles are attached as a result of opposite surface charges. Production is performed in an aqueous phase. The inorganic particles are selected from common extenders, such as kaolin, clay, talcum, mica or carbonates.
WO 2013/023018 A1 discloses a pigment blend consisting of carrier particles, pigment particles and colloidal spacer particles, whereby the spacer particles are located on the surface of the pigment particles and the pigment particles together with the spacer particles in turn are dispersed on the surface of the carrier particles.